This invention relates to blood analyzers used to measure various components in a blood sample, for example in medical diagnosis and research.
The ratio of the volume of packed red blood cells from a whole blood sample to the total sample volume is a useful measurement for diagnosing anemia and other disease conditions. That ratio usually is referred to as the "hematocrit ratio" or the "hematocrit value", and it is usually determined by centrifuging a whole blood sample to separate cells from plasma. It is known that, all other things being constant, the conductivity of a blood sample varies as a function of its hematocrit value, but other blood components, notably electrolytes, influence conductivity significantly, and the conductivity of those components must be accurately accounted for if a reliable hematocrit value is to be derived from conductivity readings.
Automated equipment for determining blood components, such as electrolyte concentration or dissolved blood gas partial pressures, often involve the use of electrodes positioned along a flow path. When whole blood is introduced in the flow path, the electrodes provide a reading of the desired blood characteristic. Currently, electrodes are available to provide electrical signals representative of various blood components such as sodium ion concentration ("[Na.sup.+ ]"), potassium ion concentration ("[K.sup.+ ]"), calcium ion concentration ("[Ca.sup.+ ]"), hydrogen ion concentration ("pH"), partial pressure attributed to O.sub.2 ("PO.sub.2 "), and partial pressure attributed to CO.sub.2 ("PCO.sub.2 "). From time to time it may be necessary to replace various components of a blood analyzer flow path, such as an electrode or a rubber inlet septum. Moreover, particularly in analyzers with a small, tortuous flow path having dead spots, whole blood may clot, resulting in lost time from shut-down, disassembly, cleaning, re-assembly, and re-starting of the apparatus.